Radio apparatus



Match 12, 1940.

v. c. MACNABB 2,192,978

RADIO APPARATUS Filed March 19, 1937 .Z' N VEN 70 E Vern n 6'. Mdcnabb.

Patented Mar. 12, 1940 UNITED S'iTES RADIO APPARATUS- poration of Illinois Application March 19,

, 3 Claims.

This'invention relates to improvements in radio apparatus, and more particularly to an improved circuit arrangement for multi-wave-band receivers.

The improvement attained by this invention is associated with the oscillator circuit of a radio receiver designed for multi-frequency reception, and among the several objects may be noted the provision of but a single energizing inductance for exciting, selectively, any one of a plurality of different frequency-range inductances in the oscillatory circuit.

Another object is found in the provision of serially related, variable capacity devices connected in circuit tuning relation to the several frequency-range inductances or windings in the oscillatory circuit, and in series with the single energizing winding for the frequency band windings.

A further object is to improve the function of a radio oscillatory circuitwhich includes selectively connectable frequency-band inductances, by arranging tuning condensers therefor in series with at least one of the inductances and in series with a single energizing coil for the inductances,

whereby to effect a strengthened and more reli able oscillation in the circuit throughout the range of each of the several frequency-bands covered by the inductances.

A still further object is attained in an improved radio oscillatory circuit having a plurality of different frequency-band windings selectively connectable to the circuit, and a single-energizing coil for said windings, the circuit arrangements being such as to permit the energizing coil to be formed of a minimum number of coil turns, whereby to reduce or minimize the reflection of capacity into the oscillating circuit resulting from the operation oi the coil.

, Referring now to the drawing which illustrates the improvements or" this invention as applied to the oscillatory circuit of a multi-wave band radio receiver, it will be noted that only this circuit portion of the radio receiving circuit is shown,

-, as it is not deemed necessary to disclose a full circuit drawing thereof. It will suffice to say that the oscillatory circuit shown may be and preferably is, of a form adaptable to radio receivers of the super-heterodyne type.

The oscillatory circuit shown includes a ther mionic valve 5 of the three electrode type, having an anode t, a cathode l and a grid element 8. Connected between the cathode l and the grid 8 are a grid leak 9 and grid condensers Ill and H,

ax these circuit elements and the described relation thereof to the tube or valve 5 being well known in the art. Selectively connectable to the grid 8 through a selector switch l2, are a plurality of different frequency-band induct- 3 ances or windings l3 and I4, two being shown in 1937, Serial No. 131,760 (01. 250-36) the present example. In the present instance, winding l3 may be so proportioned as to cover the broadcast band of frequencies, while winding 14 may cover a higher frequency band, such as the frequency range in the police call band. It is to be noted that the oscillatory circuit including the valve 5 and the inductances l3 and I4 may form the triode section of a pentagrid converter or of a separate triode or tetrode circuit, the complete circuit arrangements of which are not disclosed as such are well known in the art. However, it is pointed out that the inductances l3 and it may be associated with these circuits by coupling them either electronically, inductively or capacitively, to a first detector or modulator tube (not shown).

One terminal l5 of winding i3 is connected through a conductor I6, to a contact I? of switch 12, while thecorresponding terminal 18 of winding M is similarly connected, through a conductor ill, to another contact 253 of the switch. Thus, the switch serves to connect selectively, either of the windings l3 and Hi to the grid 8. The opposite terminal ill of winding I3 is connected to a ground terminal 22 through a lead 23, a capacitance or condenser 2 which is, by preference, of variable type as shown, a lead 25, a condenser 26 also by preferencaof variable type, and a lead 21. The opposite terminal 28 of winding M is also connected to the ground terminal 22 through a lead 29, lead 25, the variable condenser 26 and lead 21. The circuit for these frequency windings and condensers is completed to the tube cathode 1 through the ground connection 22 and a ground connection 30 for the cathode.

Inductively associated with each of the windings l3 and M is a regenerative exciting coil or anode inductance 3| which has one terminal 32 thereof connected with the tube plate or anode B through a conductor 33. The opposite terminal 34 of the coil is connected to the terminal 2i of winding it by a lead 35. Included in the lead or conductor 33 is a blocking condenser 31 which serves a purpose well known in the art. Also, in circuit with the plate or anode 6 and conductor 33 is a lead 38 which is connected to a suitable source of potential (not shown) for the tube anode or plate 6.

It will be noted from the described circuit arrangement, that the tuning condensers 24 and 26 are connected in series with respect to each other, and in series with the winding 13 and with the tube cathode I through the ground connections 22 and 30. Also, the coil 3! is returned to ground, and hence to the cathode I in the manner above described, through'the serially related condensers 24 and 26. With respect to winding I4, this is connected to ground, and hence to tube cathode I, through but one of the condensers 26. elements in the oscillatory circuit attains a marked improvement in the function of the circuit, in a manner now to be particularly pointed out.

For reasons well known to the art relating to radio circuits, the tuning condenser associated with the oscillatory circuit winding designed for response to relatively high frequency impulses, must be of a correspondingly small capacity value. Accordingly, in the present example, since winding M is responsive to higher frequencies than winding it, the tuning condenser 26 directly associated with winding H3 is of less capacity than condenser 24. Moreover, since conv densers 24 and it are in series, andas the total capacity of capacitances so related is substantialiy less than the capacity total of the condensers considered individually, these condensers must be proportioned in capacity values to attain a proper function thereof in the oscillatory circuit. This may be done by increasing the capacity value of, condenser 2 s in proportion to thereduction of total capacity of condensers 2d and Zfiresulting from their series relation. This adjustment of. the condensers is well known to the art, and hence need not be further described. The improved function of the. oscillatory circuit resulting from the described arrangement of the circuit elements, particularly with respect to the serially related condensers 2i and 2-8 and the single exciting coil 3! in series with the condensers, resides in the attainment of an strength of oscillation in the low frequency end of each of the frequency bands to which the windings i3 and I?- are responsive. Thus a more reliable and more uniform oscillatory function of the circuit is obtained. Moreover, this result obtains even though but a single exciter coil 3| is utilized to energize these windings. A further improvement results from the described connection of the exciter coil M with the series connected condensers 24 and 2t, providing a return for the oscillatory plate current through these elements in series. By this arrangement, the number of coil turns on the exciter coil ill may be reduced without decreasing the energizing function of this coil, particularly at the low frequency end of the tuning range. The benefit obtained by the reduction in number of coilturns on coil 3! is found in the minimization of a reflection of capacity from the coil into the oscillatory circuit, thereby increasing the tuning range of' this circuit.

Although the described circuit arrangement is preferred, the improved function of the oscillatory circuit could be obtained in substantially equal degree by providing a separate ground connecticn (not shown) for each of the condensers 2 3 and 2B, and by returning the coil 3i to ground through one or the other of the condensers. In all other respects, the circuit arrangement would be the same.

With the described circuit arrangement, the fun tion of the. csciliation circuit is improved in marked degree, in accordance with the foregoing objects. However, it is to be understood that the arrangement may modified without departing from the spirit and intended scope of the invention, as defined by the appended claims.

I claim:

1. An oscillator comprising a thermionic tube The described arrangement of these increased having anode, cathode and grid electrodes, a switch including a plurality of contact elements and a switch arm selectively engageable with said contact elements, a circuit connecting said switch arm to said grid electrode, a first inductance and a plurality of capacitances, circuit means connecting said inductance. and said plurality of capacitances in series between said tube cathode and one of said switch contact elements, a second inductance and circuit means connecting said second inductance between another of said switch contact elements and the connection between said capacitances, a third inductance and circuit means connecting said third inductance between said tube anode and a point contiguous tousaid first inductance away from said one. contactelement, said third inductance being, inductively coupledto said first and second inductances and being formed of a predetermined minimum number of coil turns sufficient to maintain. oscillation in the circuit at the low frequency end of the frequency range of said first two inductances.

2. An oscillator comprising a thermionic tube having anode, cathode and grid electrodes, a switch including. a, plurality of contacts and a switch arm selectively engageable with said contacts, circuit meansconnecting said'switch arm to said, tube grid, an inductance and a pair of variable capacitances, circuit means connecting said inductance and capacitances in series between said tube cathode and one of said switch contacts, said circuit. means including a conductor element connecting said pair of capacitances inserics, a second inductance connected between said, conductor element and another of said switch contacts, and a third inductance connected;between said tube anode and a point contiguous to the first said inductance away from said one contact element, said third inductance being inductively coupledto the first two inductances and further, being formed of a predetermined, minimum number of coil turns sufficient to maintain oscillation in the circuit at'the low frequency end of the frequency range of said first two inductances.

3. An oscillator comprising a thermionic tube having, anode, cathode and grid electrodes, a switchv including a plurality of switch contacts and a switch are selectively engageable with said contacts, a circuit connection between said switch arm and; said tube' grid, a plurality of inductances, aplurality of variable capacitances, circuit means connecting said capacitances and one of said inductances in series between said tube cathode and one of, said switch contacts, said circuit, means including a conductor element- 

